diff options
Diffstat (limited to 'docs/libcurl/curl_multi_fdset.3')
| -rw-r--r-- | docs/libcurl/curl_multi_fdset.3 | 21 |
1 files changed, 15 insertions, 6 deletions
diff --git a/docs/libcurl/curl_multi_fdset.3 b/docs/libcurl/curl_multi_fdset.3 index fadc53812..3dbdc4504 100644 --- a/docs/libcurl/curl_multi_fdset.3 +++ b/docs/libcurl/curl_multi_fdset.3 @@ -40,19 +40,28 @@ but be sure to FD_ZERO them before calling this function as otherwise remove any others. The \fIcurl_multi_perform(3)\fP function should be called as soon as one of them is ready to be read from or written to. -To be sure to have up-to-date results, you should call -\fIcurl_multi_perform\fP until it does not return CURLM_CALL_MULTI_PERFORM -prior to calling \fIcurl_multi_fdset\fP. This will make sure that libcurl has -updated the handles' socket states. - If no file descriptors are set by libcurl, \fImax_fd\fP will contain -1 when this function returns. Otherwise it will contain the higher descriptor number -libcurl set. +libcurl set. When libcurl returns -1 in \fImax_fd\fP, it is because libcurl +currently does something that isn't possible for your application to monitor +with a socket and unfortunately you can then not know exactly when the current +action is completed using select(). When max_fd returns with -1, you need to +wait a while and then proceed and call \fIcurl_multi_perform\fP anyway. How +long to wait? I would suggest 100 milliseconds at least, but you may want to +test it out in your own particular conditions to find a suitable value. When doing select(), you should use \fBcurl_multi_timeout\fP to figure out how long to wait for action. Call \fIcurl_multi_perform\fP even if no activity has been seen on the fd_sets after the timeout expires as otherwise internal retries and timeouts may not work as you'd think and want. + +If one of the sockets used by libcurl happens to be larger than what can be +set in an fd_set, which on POSIX systems means that the file descriptor is +larger than FD_SETSIZE, then libcurl will try to not set it. Setting a too +large file descriptor in an fd_set implies an out of bounds write which can +cause crashes, or worse. The effect of NOT storing it will possibly save you +from the crash, but will make your program NOT wait for sockets it should wait +for... .SH RETURN VALUE CURLMcode type, general libcurl multi interface error code. See \fIlibcurl-errors(3)\fP |